The present invention relates to an optical recording medium and a method of manufacturing the same. More particularly, the invention relates to a read only optical recording medium and a method of manufacturing the same.
Conventionally, optical recording mediums, such as the CD or DVD, have been widely used as recording mediums for recording digital data. The optical recording mediums can be broadly divided into ROM type optical recording mediums, such as the CD-ROM and DVD-ROM, that do not enable writing and rewriting of data, write-once type optical recording mediums, such as the CD-R and DVD-R, that enable writing but not rewriting of data, and data rewritable type optical recording mediums, such as the CD-RW and DVD-RW, that enable rewriting of data.
Among these, the ROM type optical recording medium includes a support substrate that has a pit column formed during a manufacturing process, and a reflective layer that covers the pit column. In the ROM type optical recording medium, information held by the pit column can be reproduced by irradiating a laser beam onto the reflective layer from the support substrate or an opposite side to the support substrate. An optical recording medium of this type, in which the laser beam is irradiated from the support substrate, can include a so-called CD type optical recording medium or a DVD type optical recording medium. In this case, the support substrate is generally called ‘light transmission substrate’. A thickness of the support substrate is set to about 1.1 mm in the CD type optical recording medium and to about 0.6 mm in the DVD type optical recording medium. Furthermore, a protective layer is disposed at an opposite side to the light transmission substrate as viewed from the reflective layer. The DVD type optical recording medium further includes a bonding layer and a dummy substrate having a thickness of about 0.6 mm, in addition to the protective layer.
Meanwhile, a so-called next-generation type optical recording medium, in which a laser beam in the blue wavelength region is used, is an optical recording medium in which a laser beam is irradiated from an opposite side from the support substrate. A light transmission layer, which serves as an optical path of the laser beam, is disposed at an opposite side to the support substrate as viewed from the reflective layer (see JP-A No. 2000-11453). In this case, a thickness of the support substrate is set to about 1.1 mm, and a thickness of the light transmission layer is set to about 0.1 mm.
As such, in the read only optical recording medium according to the related art, the reflective layer needs to be provided on the support substrate. This requires a vacuum process using a sputtering device during the manufacturing process. However, the vacuum process generally is high in manufacturing cost, but relatively low in production efficiency. Therefore, in order to reduce the manufacturing cost and to enhance the production efficiency, it is preferable that the read only optical recording medium is manufactured, without using the vacuum process.